Electric driving devices have been widely used in various fields. For example, in the automotive field, the electric driving devices are widely used to drive windows, door locks, tailgates and so on. The driving device of the lifting device for an automobile tailgate includes an electric motor and a gear reduction mechanism. Traditionally, the electric motor is connected with the gear reduction mechanism by an additional mounting flange. The electric motor is connected with the flange by screws. The gear reduction mechanism is fixed to the flange. However, the use of flanges undoubtedly increases the material cost and assembly cost of the lifting drive.